Artificial leather

ABSTRACT

An artificial leather is provided that has supple flexibility, moderate resilience while being dense and satisfactory thickness, where the artificial leather includes, as constituent elements, a nonwoven fabric containing ultrafine fibers having an average single-fiber diameter of 0.1 μm or more and 10 μm or less, and an elastomer, the artificial leather satisfying Formulas (a) and (b) below: 
       0.5≤ F   A   /F   B &lt;1  (a)
 
       0.5≤ F   C   /F   B &lt;1  (b)
 
     where F A , F B , and F C  are respectively the fiber density (g/cm 3 ) in a layer on one surface side, the fiber density (g/cm 3 ) in a layer at the center in the thickness direction, and the fiber density (g/cm 3 ) in a layer on the other surface side when the artificial leather is trisected in the thickness direction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase application of PCT/JP2021/030343, filed Aug. 19, 2021 which claims priority to Japanese Patent Application No. 2020-144200, filed Aug. 28, 2020, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.

FIELD OF THE INVENTION

The present invention relates to leather-like artificial leather made of a nonwoven fabric made of ultrafine fibers and an elastomer and particularly preferably relates to artificial leather that has supple flexibility and moderate resilience while being dense and having satisfactory thickness like natural leather.

BACKGROUND OF THE INVENTION

Artificial leather mainly composed of ultrafine fibers and an elastomer has excellent characteristics such as high durability and uniformity of quality in comparison with natural leather and is used not only in clothing materials but also in various fields such as vehicle interior materials, interiors, shoes, and miscellaneous goods.

Under such circumstances, various thicknesses and corresponding textures, physical properties, and a surface feel are required in order to cope with diversified applications. Various proposals have been made aiming to meet these requirements (see Patent Documents 1 to 4).

PATENT DOCUMENTS

Patent Document 1: International Publication No. 2015/037528

Patent Document 2: Japanese Patent Laid-open Publication No. 2004-91960

Patent Document 3: International Publication No. 2011/121940

Patent Document 4: International Publication No. 2017/022387

SUMMARY OF THE INVENTION

As in the techniques disclosed in Patent Documents 1 and 2, in the case where suede-like artificial leather is thinned by imparting a specific density structure or dividing the leather, a certain texture and physical properties can be achieved. However, when the thickness is adapted to various products, the texture and physical properties are not sufficient.

In addition, in Patent Document 3, by setting the density in the thickness direction to a specific ratio, it is possible to achieve a certain sense of denseness and flexibility, but moderate resilience felt together with supple flexibility of natural leather is not sufficient.

Furthermore, in Patent Document 4, it is possible to achieve the tactile sensation and the napped feel of the nubuck leather to some extent, but not only the surface feel but also the supple texture and resilience are not sufficiently imparted.

Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide artificial leather that has supple flexibility and moderate resilience while being dense and having satisfactory thickness.

As a result of intensive studies to achieve the above object, the present inventors have found that artificial leather is provided to which not only supple flexibility can be imparted, but also occurrence of creases and looseness at the time of sheet bending is suppressed, but also moderate resilience is imparted by, regarding the density of each layer when specific artificial leather is trisected in the thickness direction in an artificial leather, reducing the fiber densities in a layer on one surface side and in a layer on the other surface side and increasing the fiber density in a layer at the center in the thickness direction.

The present invention has been completed based on these findings. The present invention provides the following inventions.

The artificial leather of the present invention is artificial leather that includes, as constituent elements, a nonwoven fabric containing ultrafine fibers having an average single-fiber diameter of 0.1 μm or more and 10 μm or less, and an elastomer, the artificial leather satisfying Formulas (a) and (b) below:

0.5≤F _(A) /F _(B)<1  (a)

0.5≤F _(C) /F _(B)<1  (b)

where F_(A), F_(B), and F_(C) are respectively the fiber density (g/cm³) in a layer on one surface side, the fiber density (g/cm³) in a layer at the center in the thickness direction, and the fiber density (g/cm³) in a layer on the other surface side when the artificial leather is trisected in the thickness direction.

In a preferred aspect of the artificial leather of the present invention, the artificial leather includes at least one nap layer formed by nap raising.

In a preferred aspect of the artificial leather of the present invention, the artificial leather further includes at least one resin layer.

In a preferred aspect of the artificial leather of the present invention, the resin layer is discontinuously formed in the surface of the artificial leather.

In a preferred aspect of the artificial leather of the present invention, the artificial leather further satisfies Formulas (c) and (d) below:

0.6≤P _(A) /P _(B)<1  (c)

0.6≤P _(C) /P _(B)<1  (d)

where P_(A), P_(B), and P_(C) are respectively the elastomer density (g/cm³) in the layer on one surface side, the elastomer density (g/cm³) in the layer at the center in the thickness direction, and the elastomer density (g/cm³) in the layer on the other surface side when the artificial leather is trisected in the thickness direction.

In a preferred aspect of the artificial leather of the present invention, the overall density of the artificial leather is 0.2 g/cm³ or more and 0.7 g/cm³ or less.

In a preferred aspect of the artificial leather of the present invention, the thickness of the artificial leather is 0.8 mm or more and 4.0 mm or less.

According to the present invention, it is possible to obtain artificial leather that has supple flexibility and moderate resilience while being dense and having satisfactory thickness. In particular, since the artificial leather of the present invention has specific densities in the thickness direction, creases and looseness occurring when the artificial leather is bent are suppressed, and thus the artificial leather can be used in various fields such as clothing, vehicle interior materials, furniture interior materials, building materials, shoes, bags, and miscellaneous goods, particularly suitably in shoes, bags, and miscellaneous goods applications in which natural leather-like appearance and texture are required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view schematically illustrating one embodiment of a cross section of artificial leather of the present invention.

FIG. 2 is a schematic plan view illustrating a form of a surface in one embodiment of the artificial leather of the present invention.

FIG. 3 is a schematic cross-sectional view schematically illustrating another embodiment of a cross section of the artificial leather of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The artificial leather of the present invention is artificial leather that includes, as constituent elements, a nonwoven fabric containing ultrafine fibers having an average single-fiber diameter of 0.1 μm or more and 10 μm or less, and an elastomer, the artificial leather satisfying Formulas (a) and (b) below:

0.5≤F _(A) /F _(B)<1  (a)

0.5≤F _(C) /F _(B)<1  (b)

where F_(A), F_(B), and F_(C) are respectively the fiber density (g/cm³) in a layer on one surface side, the fiber density (g/cm³) in a layer at the center in the thickness direction, and the fiber density (g/cm³) in a layer on the other surface side when the artificial leather is trisected in the thickness direction.

Hereinafter, details will be described, but the present invention is not limited to the scope described below at all as long as the gist thereof is not exceeded.

[Nonwoven Fabric]

The artificial leather of the present invention includes, as a constituent element, the nonwoven fabric containing ultrafine fibers having an average single-fiber diameter of 0.1 μm or more and 10 μm or less.

As the ultrafine fibers constituting the nonwoven fabric according to the artificial leather of the present invention, synthetic fibers are preferably used in order to obtain artificial leather excellent in mechanical strength, heat resistance, and light resistance. Examples of the synthetic fibers include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, and polylactic acid; polyamides such as polyamide 6 and polyamide 66; and other various synthetic fibers such as acrylic, polyethylene, polypropylene, and thermoplastic cellulose. Among the above synthetic fibers, polyester fibers and polyamide fibers are particularly preferably used. Among these, fibers made of polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate are particularly preferred from the viewpoint of high strength, dimensional stability, light resistance, and dyeing properties. Furthermore, when synthetic fibers are used as fibers constituting the nonwoven fabric, fibers containing recycled raw materials or components derived from biomass resources may be used from the viewpoint of caring for the environment. Furthermore, ultrafine fibers of different materials may be mixed.

As for the component derived from a biomass resource, when polyester fibers are used as the synthetic fibers, a component derived from a biomass resource may be used as a dicarboxylic acid as a raw material of the polyester and/or an ester-forming derivative thereof. As a diol, a component derived from a biomass resource may be used. From the viewpoint of reducing the environmental load, it is preferable to use components derived from biomass resources for both the dicarboxylic acid and/or the ester-forming derivative thereof and the diol.

Examples of the dicarboxylic acid that can be used as a raw material when a polyester is used as the synthetic fibers include aromatic dicarboxylic acids such as “terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid (such as 2,6-naphthalenedicarboxylic acid), diphenyldicarboxylic acid (such as diphenyl-4,4′-dicarboxylic acid)”; aliphatic dicarboxylic acids such as “oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and dodecanedioic acid”; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; and aromatic dicarboxylic acid salts such as “5-sulfoisophthalate salts (such as 5-sulfoisophthalic acid lithium salt, 5-sulfoisophthalic acid potassium salt, and 5-sulfoisophthalic acid sodium salt)”.

Examples of the ester-forming derivative of a dicarboxylic acid serving as the raw material of the polyester include lower alkyl esters of dicarboxylic acid, acid anhydrides, and acyl chlorides. Specifically, methyl esters, ethyl esters, hydroxyethyl esters, and the like are preferably used.

Examples of the diol include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, cyclohexanedimethanol, diethylene glycol, 2-methyl-1,3-propanediol, a polyoxyalkylene glycol (such as polyethylene glycol) having a molecular weight of 500 or more and 20,000 or less, and an ethylene oxide adduct of bisphenol A.

When polyamide fibers are used as the synthetic fibers, polyamide 6, polyamide 66, polyamide 56, polyamide 610, polyamide 11, polyamide 12, copolymerized polyamide, and the like can be used. Among them, polyamide 56, polyamide 610, and polyamide 11, which easily contain components derived from biomass resources, are preferably used.

In the case where synthetic fibers are used as the fibers constituting the nonwoven fabric, the polymer forming the fibers may contain inorganic particles such as titanium oxide particles, a lubricant, a pigment, a thermal stabilizer, an ultraviolet absorber, a conductive agent, a heat storage agent, an antimicrobial agent, and the like in accordance with various purposes.

The average single-fiber diameter of the ultrafine fibers is 0.1 μm or more and 10 μm or less. Setting the average single-fiber diameter to 10.0 μm or less, preferably 7.0 μm or less, more preferably 4.0 μm or less, serves to obtain artificial leather having highly fine, soft-to-the-touch surface quality. Meanwhile, setting the average single-fiber diameter to 0.1 μm or more, preferably 1.0 μm or more, more preferably 1.5 μm or more, has an excellent effect on the color developability and fastness after dyeing.

In the present invention, the average single-fiber diameter is a value calculated by taking a scanning electron microscope (SEM) photograph of a cross-section of the artificial leather, randomly selecting 50 ultrafine fibers having a circular shape or an elliptical shape close to a circular shape, measuring the single-fiber diameters, calculating the arithmetic average of the 50 fibers, and rounding the arithmetic average off to the first decimal place when expressed in μm. When the ultrafine fibers have a deformed cross-sectional shape, the cross-sectional areas of single fibers are measured first, and the equivalent circle diameters are calculated to determine the single-fiber diameters.

As for the cross-sectional shape of the ultrafine fibers, a circular cross section is applicable though fibers having cross sections of other shapes such as an ellipse, a flat shape, a polygon such as a triangle, a sector, or a cross may also be adopted.

The nonwoven fabric used in the present invention may be either a filament nonwoven fabric or a staple nonwoven fabric. In a preferred aspect, a staple nonwoven fabric is employed because the number of napped hairs on the product surface is large and an elegant appearance is easily obtained.

The fiber length of the ultrafine fibers in the case where a staple nonwoven fabric is used is preferably 25 mm or more and 90 mm or less. Setting the fiber length to 90 mm or less ensures high quality and good texture while setting the fiber length to 25 mm or more serves to obtain artificial leather with high wear resistance. The fiber length is more preferably 35 mm or more and 80 mm or less, still more preferably 40 mm or more and 70 mm or less.

The basis weight of the nonwoven fabric used in the present invention is preferably 50 g/m² or more and 1,000 g/m² or less. When the basis weight of the nonwoven fabric is 50 g/m² or more, more preferably 80 g/m² or more, the artificial leather is less likely to be paper-like, and artificial leather excellent in texture can be obtained. On the other hand, when the basis weight of the nonwoven fabric is 1,000 g/m² or less, more preferably 900 g/m² or less, the texture of the artificial leather is less likely to be hard but becomes soft.

The basis weight of the nonwoven fabric is measured according to “6.2 Mass per unit area” in “Test methods for nonwovens” specified in JIS L 1913: 2010.

In the nonwoven fabric used in the present invention, a woven fabric may be laminated inside or on one side of the nonwoven fabric and entangled and integrated for the purpose of improving strength and form stability.

As the type of fibers constituting the woven fabric used when the woven fabric is entangled and integrated, a filament, a spun yarn, an innovative spun yarn, a mixed composite yarn of a filament and a spun yarn, and the like can be used. A large number of fuzzes are present on the surface of the spun yarn due to its structure, and when the nonwoven fabric and the woven fabric are entangled with each other, if the fuzzes fall off and are exposed to the surface, defects are likely to occur. Therefore, it is more preferable to use a filament, and it is preferable to use a multifilament as the filament.

The average single-fiber diameter of the fibers constituting the woven fabric is preferably 1 μm or more and 50 μm or less. When the average single-fiber diameter of the fibers constituting the woven fabric is 50 μm or less, artificial leather excellent in flexibility is obtained, and when the average single-fiber diameter is 1 μm or more, the form stability of a product as the artificial leather is improved.

The average single-fiber diameter of the fibers constituting the woven fabric used in the present invention is measured in the same manner as the method for measuring the average single-fiber diameter of the ultrafine fibers described above.

The total fineness of the yarns constituting the woven fabric is measured according to “8.3.1 Fineness based on corrected mass b) Method B (simplified method)” in “Testing methods for man-made filament yarns” specified in JIS L 1013: 2010 and is preferably 30 dtex or more and 170 dtex or less. When the total fineness is 170 dtex or less, artificial leather excellent in flexibility is obtained, and when the total fineness is 30 dtex or more, the form stability of a product as the artificial leather is improved. The multifilaments of the warp and the weft preferably have the same total fineness.

The component of the fibers constituting the woven fabric is preferably the same as the constituent of the nonwoven fabric, and from the viewpoint of reducing the environmental load, it is preferable to contain a component derived from a biomass resource.

In particular, in the nonwoven fabric of the artificial leather according to the present invention, the ultrafine fibers constituting the nonwoven fabric, or the woven fabric, the biomass plastic content defined by ISO 16620 (2015) is preferably 5% or more and 100% or less. Since the environmental load can be further reduced, or the fiber tenacity of the ultrafine fibers in the artificial leather and the abrasion resistance of the artificial leather are improved, the biomass plastic content of the nonwoven fabric is more preferably 15% or more, still more preferably 25% or more.

When the woven fabric is laminated inside or on one side of the nonwoven fabric and entangled and integrated as described above, the biomass plastic content of the product obtained by integrating the nonwoven fabric and the woven fabric is referred to as the “biomass plastic content of the nonwoven fabric”.

In the present invention, the biomass plastic contents of the nonwoven fabric and the artificial leather are measured as follows.

(1) ISO 16620-2 is used to measure the biobased carbon content in the entire carbon in the components constituting a sample.

(2) The sample-constituting components and their component ratio are identified.

Note that for the identification, it is possible to use a known method such as GC-MS, NMR, and element analysis.

(3) From the results of (1) and (2), the component derived from a biomass resource is specified.

(4) The percentage (mass ratio) of the component derived from a biomass resource among the components of the sample is calculated as the biomass plastic content of the sample.

When the biomass plastic content of the nonwoven fabric is measured from the artificial leather, it is possible to appropriately adopt, depending on the constituents of the artificial leather, for instance, a method of extracting and isolating a component of the nonwoven fabric by using a solvent that dissolves only the nonwoven fabric or, by contrast, a method of removing the elastomer and the resin layer by using a solvent that dissolves these components from the artificial leather.

As a method of removing components other than the nonwoven fabric from the artificial leather, for example, a method of extracting components including the elastomer and the resin layer using N,N-dimethylformamide heated to 60° C. or higher and 100° C. or lower can be used.

[Elastomer]

Furthermore, the artificial leather of the present invention includes the nonwoven fabric and the elastomer as constituent elements.

The elastomer used in the present invention mainly serves as a binder for holding the nonwoven fabric that is a constituent element of the artificial leather. In order to obtain artificial leather having a flexible texture, polyurethane, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), acrylic resin, and the like can be used as the elastomer. In particular, polyurethane is preferably used as a main component. Use of polyurethane provides artificial leather having a dense tactile sensation, a leather-like appearance, and physical properties enough to endure actual use. In addition, the “main component” as used herein means that the mass of polyurethane is more than 50 mass % based on the mass of the whole elastomer.

Use of the elastomer provides artificial leather having a dense tactile sensation, a leather-like appearance, and physical properties enough to endure actual use.

In the case where polyurethane is used in the present invention, either organic solvent-based polyurethane used in the state of being dissolved in an organic solvent or water-dispersed polyurethane used in the state of being dispersed in water can be used. The polyurethane used is preferably polyurethane obtained by a reaction of a polymer diol, an organic diisocyanate, and a chain extender. In addition, from the viewpoint of reducing the environmental load, it is preferable to contain a component derived from a biomass resource. In particular, in the case where polyurethane is used as the elastomer, as the component derived from a biomass resource, a component derived from a biomass resource is preferably used as the polymer diol, a raw material derived from a biomass resource of which is relatively easily obtained, among the constituents. Hereinafter, a preferred aspect of each component constituting polyurethane when polyurethane is used as the elastomer in the present invention will be further described.

<Polymer Diol>

When polyurethane is used as the elastomer, as a suitable polymer diol, at least one polymer diol selected from polyester diols, polyether diols, and polycarbonate diols or from polymer diols such as polyester diols and polyether diols can be used, but it is preferable to contain a polycarbonate diol excellent in hydrolysis resistance.

A polycarbonate-based diol as described above can be produced, for example, through an ester exchange reaction between an alkylene glycol and a carbonate ester or through a reaction of phosgene or a chloroformate ester with an alkylene glycol.

Examples of the alkylene glycol include linear alkylene glycols such as “ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, and 1,10-decanediol”; branched alkylene glycols such as “neopentyl glycol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, and 2-methyl-1,8-octanediol”; alicyclic diols such as 1,4-cyclohexanediol; aromatic diols such as bisphenol A; and others such as glycerin, trimethylolpropane, and pentaerythritol. For the present invention, each of these diols may be either a polycarbonate-based diol produced from a single alkylene glycol or a copolymerized polycarbonate-based diol produced from two or more types of alkylene glycols.

Examples of the polyester-based diols include polyester diols produced by condensing one of various low molecular weight polyols and a polybasic acid.

For example, one or a plurality selected from the following can be used as the low molecular weight polyol described above: ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,2-dimethyl-1,3-propanediol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,8-octanediol, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, cyclohexane-1,4-diol, and cyclohexane-1,4-dimethanol. Furthermore, an adduct formed by adding one of various alkylene oxides to bisphenol A is also usable.

Furthermore, for example, one or a plurality selected from the following can be used as the polybasic acid described above: succinic acid, maleic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, phthalic acid, isophthalic acid, terephthalic acid, and hexahydroisophthalic acid.

Examples of the aforementioned polyether-based diols include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and copolymerized diols formed by combining these substances.

A polymer diol to be used for the present invention preferably has a number average molecular weight of 500 or more and 4,000 or less. The number average molecular weight should preferably be 500 or more, more preferably 1,500 or more, to prevent the resulting artificial leather from having stiff texture. Furthermore, a number average molecular weight of preferably 4,000 or less, more preferably to 3,000 or less, allows the polyurethane to maintain a required inherent strength.

Note that in the case of using a component derived from a biomass resource in the above polymer diol, the polymer diol may consist of the component derived from a biomass resource or may include a copolymer containing a polymer diol derived from a biomass resource and a polymer diol derived from an oil resource. From the viewpoint of reducing an environmental load, it is preferable that the amount of the polymer diol derived from a biomass resource is larger than that of the polymer diol derived from an oil resource.

<Organic Diisocyanate>

In the case where polyurethane is used as the elastomer, examples of usable organic diisocyanates include aliphatic diisocyanates such as “hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and xylylene diisocyanate”; and aromatic diisocyanates such as “4,4′-diphenylmethane diisocyanate and tolylene diisocyanate”, which may be used in combination. In particular, the use of aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate is preferred when durability and heat resistance are important, while the use of aliphatic diisocyanates such as hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate is preferred when light resistance is important. One of these organic diisocyanates may be used, or two or more of these organic diisocyanates may be used in combination.

<Chain Extender>

When polyurethane is used as the elastomer, suitable chain extenders include at least one low molecular weight compound having two or more active hydrogen atoms, such as water, ethylene glycol, butanediol, ethylenediamine, and 4,4′-diaminodiphenylmethane. In addition, from the viewpoint of reducing the environmental load, it is preferable to use a chain extender containing a component derived from a biomass resource.

<Crosslinker>

In the case where polyurethane is used as the elastomer, a crosslinker may be used in combination for the purpose of improving waterproofness, wear resistance, hydrolysis resistance, and the like, as required. The crosslinker may be either an external crosslinker to be added to polyurethane as a third component or an internal crosslinker that contains a reaction point acting as a crosslinking structure in the polyurethane molecular structure. For the present invention, it is preferable to use an internal crosslinker because crosslinking points can be formed uniformly in the polyurethane molecular structure, thereby mitigating the reduction in flexibility.

A compound containing an isocyanate group, an oxazoline group, a carbodiimide group, an epoxy group, a melamine resin, or a silanol group can be used as the aforementioned crosslinker. However, as crosslinking progresses excessively, polyurethane tends to harden, resulting in artificial leather with stiff texture. Therefore, the use of a crosslinker containing a silanol group is preferred from the viewpoint of the balance between reactivity and flexibility.

If a water-dispersed polyurethane is used for the present invention, it is preferable to adopt an internal emulsifier to allow the polyurethane to be dispersed in water. Examples of the internal emulsifier include cationic ones such as quaternary amine salts; anionic ones such as sulfonate salts and carboxylate salts; nonionic ones such as polyethylene glycol; combinations of cationic and nonionic ones; and combinations of anionic and nonionic ones. In particular, nonionic internal emulsifiers are preferred because they are higher in light resistance than cationic internal emulsifiers and free of problems attributed to neutralization agents as compared to anionic internal emulsifiers.

<Other Additives>

The elastomer may contain various additives including pigments such as carbon black; flame retardants such as phosphorus, halogen, and inorganic flame retardants; antioxidants such as phenolic, sulfur, and phosphorus antioxidants; ultraviolet absorbers such as benzotriazole, benzophenone, salicylate, cyanoacrylate, and oxalic acid anilide ultraviolet absorbers; light stabilizers such as hindered amine and benzoate light stabilizers; hydrolysis stabilizers such as polycarbodiimide; plasticizers; antistatic agents; surfactants; coagulation modifiers; and dyes according to the purpose.

The elastomer used for the present invention may contain elastomer resins, such as polyester-based, polyamide-based, and polyolefin-based ones, acrylic resins, and ethylene-vinyl acetate resins unless they impair the texture or performance thereof as a binder.

The content of the elastomer in the artificial leather can be appropriately adjusted in consideration of the kind of the elastomer used, the method for manufacturing the elastomer, and the texture and physical properties. The content of the elastomer is preferably 10 mass % or more and 60 mass % or less with respect to the mass (which refers to the total mass of the nonwoven fabric and the woven fabric when the nonwoven fabric is entangled and integrated with the woven fabric) of the nonwoven fabric. By setting the content of the elastomer to preferably 10 mass % or more, more preferably 15 mass % or more, still more preferably 20 mass % or more, with respect to the mass of the nonwoven fabric, the bonding between the fibers constituting the nonwoven fabric by the elastomer can be enhanced, and the abrasion resistance of the artificial leather can be improved. On the other hand, by setting the content of the elastomer to preferably 60 mass % or less, more preferably 45 mass % or less, still more preferably 40 mass % or less, with respect to the mass of the nonwoven fabric, the texture of the artificial leather can be made flexible.

In the elastomer of the artificial leather in the invention, the biomass plastic content defined according to ISO 16620 (2015) is preferably 5% or more and 100% or less. Since the environmental load can be further reduced, or the texture of the artificial leather is improved, the biomass plastic content of the elastomer is more preferably 15% or more, still more preferably 25% or more.

Examples of a method for separating the elastomer from the artificial leather to measure the biomass plastic content of the elastomer include a method of extracting and isolating a component of the elastomer by using a solvent that dissolves only the elastomer or, by contrast, a method of removing the ultrafine fibers and the resin layer from the artificial leather by using a solvent that dissolves these components. An appropriate method can be adopted depending on the constituent components of the artificial leather. The other points are basically measured by the same method as for the biomass plastic content of the nonwoven fabric described above.

When the elastomer is soluble in an organic solvent, the elastomer can be extracted and isolated with an organic solvent such as N,N-dimethylformamide. When the elastomer is obtained from a water-dispersed material, a method of removing fibers using a solvent (in the case of a polyester, 1,1,1,3,3,3-hexafluoro-2-propanol, ortho-chlorophenol, or the like) that dissolves the fibers is exemplified. In addition, a method of decomposing and extracting the elastomer that has been in a water-dispersed state using N,N-dimethylformamide heated to 60° C. or higher and 100° C. or lower can be used.

When the resin layer to be described later is dissolved in a solvent similar to that for the elastomer, the elastomer can be isolated by the above-described method by slicing or peeling and removing the resin layer in advance.

[Artificial Leather]

The artificial leather of the present invention is artificial leather that includes, as constituent elements, the above nonwoven fabric and the above elastomer, the artificial leather satisfying Formulas (a) and (b) below.

0.5≤F _(A) /F _(B)<1  (a)

0.5≤F _(C) /F _(B)<1  (b)

where F_(A), F_(B), and F_(C) are respectively the fiber density (g/cm³) in a layer on one surface side, the fiber density (g/cm³) in a layer at the center in the thickness direction, and the fiber density (g/cm³) in a layer on the other surface side when the artificial leather is trisected in the thickness direction.

That is, it is important to lower the fiber densities in the layer on one surface side and the layer on the other surface side and to increase the fiber density in the layer at the center in the thickness direction.

By reducing the fiber density in the layer on one surface side with respect to that in the layer at the center in the thickness direction as shown in Formula (a), the surface will be nap-raised easily and have fine, soft-to-the-touch surface quality. In addition, it is possible to impart supple flexibility to the artificial leather. Furthermore, by reducing the fiber density in the layer on the other surface side with respect to that in the layer at the center in the thickness direction as shown in Formula (b) above, supple flexibility can be imparted to the artificial leather. By reducing the fiber densities in the layer on one surface side and the layer on the other surface side with respect to that in the layer at the center in the thickness direction as shown in Formulas (a) and (b), not only supple flexibility can be imparted, but also occurrence of creases and looseness at the time of bending the sheet can be suppressed. On the other hand, by increasing the fiber density in the layer at the center in the thickness direction, moderate resilience can be imparted to the artificial leather. Specifically, by setting the fiber density ratio (F_(A)/F_(B) or F_(C)/F_(B)) to less than 1, preferably 0.95 or less, more preferably 0.9 or less, still more preferably 0.85 or less, particularly preferably 0.8 or less, the one surface will be nap-raised easily and have fine, soft-to-the-touch surface quality. When the fiber density ratio is 0.5 or more, preferably 0.6 or more, more preferably 0.65 or more, both of supple flexibility and resilience can be achieved.

In the present invention, F_(A), F_(B), and F_(C) can each be measured as follows. As described below, the fiber density referred to in the present invention indicates the density of a fiber structure including ultrafine fibers and a woven fabric constituting a nonwoven fabric when the woven fabric is laminated inside or on one side of the nonwoven fabric and entangled and integrated.

(1) A sample measuring 20 cm×20 cm of the artificial leather is trisected in the thickness direction.

(2) As illustrated in FIG. 1 , artificial leather 11 is divided into a layer (A) on one surface side, a layer (B) at the center in the thickness direction, and a layer (C) on the other surface side. When the nap layer is formed in the layer (A) on the surface side, the trisection in the thickness direction is performed including the nap layer. As shown in FIG. 3 , when the resin layer is disposed on the nap layer in the layer (A) on one surface side, a portion including the resin layer is defined as a layer (D) on one surface side, and division into a layer (E) at the center in the thickness direction and a layer (F) on the other surface side is performed in the same manner. Then, the divided sample is immersed in N,N-dimethylformamide for eight hours to completely extract the elastomer.

(3) The sample was sufficiently dried, the mass of the dried sample was measured, and the fiber density in each layer was calculated by the following formula.

Fiber density (g/cm³)=mass of sample after extraction (g)/(20 (cm)×20 (cm)×thickness of sample before extraction (cm))

For the thickness of the sample before extraction, 10 images of different portions of a cross section of the sample before extraction were photographed at a magnification of 200 times using a scanning electron microscope, and the thickness of the sample was determined from each of these photographed images. When the sample had a nap layer, the thickness excluding the thickness of the nap layer was taken as the thickness of the sample.

(4) Using the calculated F_(A), F_(B), and F_(C), the fiber density ratio (F_(A)/F_(B) or F_(C)/F_(B)) is calculated, and the average of the values measured at 10 points is taken as the result.

The artificial leather of the present invention preferably includes at least one nap layer formed by nap raising. By providing the nap layer, a tactile sensation of the surface like natural leather can be obtained, and adhesiveness to the resin layer described later is excellent. Furthermore, the nap fibers exposed on the surface of the artificial leather including a resin layer discontinuously formed can provide a surface tactile sensation closer to that of natural leather.

The artificial leather of the present invention also preferably includes at least one resin layer. By providing the resin layer, it is possible to obtain a full grain or nubuck natural leather-like surface tactile sensation. In this case, the resin layer is also preferably formed discontinuously in the surface of the artificial leather.

By discontinuously forming the resin layer, sufficient air permeability of the artificial leather is secured in a nap portion that is a portion where a non-resin layer does not exist and where a portion of the nap layer is exposed, and when the artificial leather is bent, cracking of the resin layer does not occur, and good quality and texture can be maintained.

In the present invention, “the resin layer is discontinuously formed in the surface of the artificial leather” means a state in which a resin layer 2 including the layered resin scattered in an island shape is disposed on a nap layer 1 continuously existing even under the resin layer 2 on the surface of the artificial leather when viewed from above the artificial leather as illustrated in FIG. 2 . In the observation from above, a state in which the resin layer and the exposed nap portion exist, such as the case where the resin layer 2 is surrounded by the nap layer 1 and has an isolated shape, is also included. A cross section of the artificial leather in this case is illustrated in FIG. 3 . In addition, the resin layer 2 scattered in an island shape may be regularly present, but the shape and arrangement of the resin layer 2 are preferably random in order to obtain a surface feel closer to that of natural leather due to the random shape and arrangement.

The area ratio of the resin layer to the surface of the artificial leather is preferably 10 to 90%. By setting this ratio to 10% or more, preferably 20% or more, it is possible to obtain resin layer-containing artificial leather excellent in abrasion resistance and having a surface feel and tactile sensation like a nubuck-like or grained surface. On the other hand, when the ratio is 90% or less, preferably 80% or less, air permeability and a napped feel like a suede-like base material can be imparted to the resin layer-containing artificial leather.

The resin layer is preferably constituted of at least two layers. More preferably, it is constituted of at least three layers. More preferably, the resin layer has a three-layer structure of an adhesive layer, an intermediate layer, and a surface layer. Here, the adhesive layer has a function of bonding the fiber structure and the intermediate layer. The adhesive layer is a resin layer excellent in adhesion to the fibers of the nap layer in which the ultrafine fibers of the fiber structure are nap-raised and the intermediate layer, and when the adhesive layer is present between these layers, adhesion between the fiber structure and the resin layer is enhanced, so that artificial leather excellent in abrasion resistance is obtained.

In addition, if there are two or more resin layers, it is possible to obtain artificial leather having excellent abrasion resistance for an automobile seat, a sofa, or the like, which require more durability. When there is one resin layer, abrasion resistance is poor.

The resin used in the resin layer preferably has stretchable rubber elasticity, and examples thereof include polyurethane, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), and acrylic resin. Among them, a material containing polyurethane as a main component, specifically a material containing polyurethane in an amount of 50 mass % or more, is preferably used from the viewpoint of achieving a balance between texture and physical properties.

As described above, there are various types of polyurethane including organic solvent-soluble ones that are used in a state of being dissolved in an organic solvent and water-dispersed ones that are used in a state of being dispersed in water, both of which can work for the present invention.

Polyurethane obtained by a reaction of a polymer diol, an organic diisocyanate, and a chain extender is preferred as polyurethane to be used for the resin layer in the present invention. In addition, from the viewpoint of reducing the environmental load, it is preferable to contain a component derived from a biomass resource. In particular, in the case where polyurethane is used as the resin used for the resin layer, as the component derived from a biomass resource, a component derived from a biomass resource is preferably used as the polymer diol, a raw material derived from a biomass resource of which is relatively easily obtained, among the constituents. Hereinafter, a preferred aspect of each component constituting polyurethane when polyurethane is used as the resin used for the resin layer in the present invention will be further described.

<Polymer Diol>

In the case where polyurethane is used for the resin layer, examples of a suitable polymer diol include polycarbonate diols, polyester diols, polyether diols, silicone-based diols, fluorine-based diols, and copolymers in which these diols are combined. Among them, from the viewpoint of light resistance, a polycarbonate diol and a polyester diol are preferably used. Further, in the viewpoint of hydrolysis resistance and heat resistance, a polycarbonate diol is preferably used. In the adhesive layer, a polyether diol or a polyester diol is preferably used from the viewpoint of adhesion to the surface of the artificial leather.

The polycarbonate-based diol can be produced, for example, through an ester exchange reaction between an alkylene glycol and a carbonate ester or through a reaction of phosgene or a chloroformate ester with an alkylene glycol.

Examples of the alkylene glycol include linear alkylene glycols such as “ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, and 1,10-decanediol”; branched alkylene glycols such as “neopentyl glycol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, and 2-methyl-1,8-octanediol”; alicyclic diols such as 1,4-cyclohexanediol; aromatic diols such as bisphenol A; glycerin; trimethylolpropane; and pentaerythritol.

In the present invention, either a polycarbonate diol obtained from a single alkylene glycol or a copolymerized polycarbonate diol obtained from two or more alkylene glycols can be used.

<Organic Diisocyanate>

In the case where polyurethane is used as the resin used for the resin layer, examples of the organic diisocyanate that reacts with a suitable polymer diol include aliphatic diisocyanates such as “hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate, and xylylene diisocyanate”; and aromatic diisocyanates such as “4,4′-diphenylmethane diisocyanate and tolylene diisocyanate”. These may be combined. Among them, when durability and heat resistance are emphasized, an aromatic polyisocyanate such as 4,4′-diphenylmethane diisocyanate is preferable. Among them, when light resistance is emphasized, aliphatic polyisocyanates such as hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and isophorone diisocyanate are preferable. One of these organic diisocyanates may be used, or two or more of these organic diisocyanates may be used in combination.

<Chain Extender>

When polyurethane is used for the resin layer, suitable chain extenders include at least one low molecular weight compound having two or more active hydrogen atoms, such as water, ethylene glycol, butanediol, ethylenediamine, and 4,4′-diaminodiphenylmethane.

<Other Additives>

The resin used for the resin layer in the present invention may contain elastomer resins, such as polyester-based, polyamide-based, and polyolefin-based ones, acrylic resins, and ethylene-vinyl acetate resins unless they impair the abrasion resistance or texture. These resins may contain various additives including pigments such as carbon black; flame retardants such as phosphorus, halogen, and inorganic flame retardants; antioxidants such as phenolic, sulfur, and phosphorus antioxidants; light stabilizers such as hindered amine and benzoate light stabilizers; hydrolysis stabilizers such as polycarbodiimide; plasticizers; antistatic agents; surfactants; coagulation modifiers; and dyes.

The thickness of the resin layer is not particularly limited, but the total thickness thereof is preferably 0.001 mm or more and 0.500 mm or less. When the total thickness is 0.001 mm or more, more preferably 0.010 mm or more, still more preferably 0.050 mm or more, resin layer-containing artificial leather excellent in abrasion resistance can be obtained. On the other hand, when the total thickness is 0.500 mm or less, more preferably 0.400 mm or less, still more preferably 0.300 mm or less, resin layer-containing artificial leather having flexible texture can be obtained.

The thickness of each resin layer is preferably 0.001 mm or more and 0.200 mm or less for a first layer and a second layer and is preferably 0.008 mm or more and 0.300 mm or less for a third layer.

In the present invention, the total thickness of the resin layer of the artificial leather is measured as follows.

(1) A cross section perpendicular to the surface direction and the machine direction of the artificial leather is cut out and placed on a sample stage so that the cross section is not distorted.

(2) Using a scanning electron microscope, 10 images of cross sections of a sample piece of the artificial leather are photographed at different positions at a magnification of 200 times.

(3) From each of these photographed images, a distance between two points of a highest position z1 of the resin layer and a lowest position z2 of the resin layer when a direction parallel to the cross section is regarded as the horizontal direction, the nap layer side of the cross section is regarded as the upside, and the other surface is regarded as the downside is acquired, and the total thickness of the resin layer is calculated.

(4) The average of 10 values obtained by the calculation is taken as the total thickness of the resin layer.

The artificial leather of the present invention preferably further satisfies Formulas (c) and (d) below.

0.6≤P _(A) /P _(B)<1  (c)

0.6≤P _(C) /P _(B)<1  (d)

where P_(A), P_(B), and P_(C) are respectively the elastomer density (g/cm³) in the layer on one surface side, the elastomer density (g/cm³) in the layer at the center in the thickness direction, and the elastomer density (g/cm³) in the layer on the other surface side when the artificial leather is trisected in the thickness direction.

That is, as with the fiber density, it is preferable to lower the elastomer densities in the layer on one surface side and the layer on the other surface side and to increase the elastomer density in the layer at the center in the thickness direction.

By reducing the elastomer density in the layer on one surface side with respect to that in the layer at the center in the thickness direction as shown in Formula (c), the surface will be nap-raised easily and have fine, soft-to-the-touch surface quality. In addition, it is possible to impart supple flexibility to the artificial leather. Furthermore, by reducing the elastomer density in the layer on the other surface side with respect to that in the layer at the center in the thickness direction as shown in Formula (d) above, supple flexibility can be imparted to the artificial leather. By reducing the elastomer densities in the layer on one surface side and the layer on the other surface side with respect to that in the layer at the center in the thickness direction as shown in Formulas (c) and (d), not only supple flexibility can be imparted, but also occurrence of creases and looseness at the time of bending the sheet can be suppressed. On the other hand, by increasing the elastomer density in the layer at the center in the thickness direction, moderate resilience can be imparted to the artificial leather. Specifically, by setting the elastomer density ratio (P_(A)/P_(B) or P_(C)/P_(B)) to less than 1, preferably 0.95 or less, more preferably 0.9 or less, still more preferably 0.85 or less, particularly preferably 0.8 or less, the surface will be nap-raised easily and have fine, soft-to-the-touch surface quality. When the elastomer density ratio is 0.6 or more, preferably 0.7 or more, more preferably 0.75 or more, both of supple flexibility and resilience can be achieved.

In the present invention, P_(A), P_(B), and P_(C) can each be measured as follows.

(1) A sample measuring 20 cm×20 cm of the artificial leather is trisected in the thickness direction.

(2) As illustrated in FIG. 1 , division into a layer (A) on one surface side, a layer (B) at the center in the thickness direction, and a layer (C) on the other surface side is performed. As shown in FIG. 3 , when the resin layer is disposed on the nap layer in the layer (A) on one surface side, a portion including the resin layer is defined as a layer (D) on one surface side, and division into a layer (E) at the center in the thickness direction and a layer (F) on the other surface side is performed in the same manner. At this time, the resin layer present in the layer (D) on one surface side is removed. Then, the divided sample is immersed in N,N-dimethylformamide for eight hours to completely extract the elastomer.

(3) The sample was sufficiently dried, the mass of the dried sample was measured, and the elastomer density in each layer was calculated by the following formula.

Elastomer density (g/cm³)=(mass of sample before extraction (g)−mass of sample after extraction (g))/(20 (cm)×20 (cm)×thickness of sample before extraction (cm))

For the thickness of the sample before extraction, 10 images of different portions of a cross section of the sample before extraction were photographed at a magnification of 200 times using a scanning electron microscope, and the thickness of the sample was determined from each of these photographed images. When the sample had a nap layer, the thickness excluding the thickness of the nap layer was taken as the thickness of the sample.

(4) Using the calculated P_(A), P_(B), and P_(C), the elastomer density ratio (P_(A)/P_(B) or P_(C)/P_(B)) is calculated, and the average of the values measured at 10 points is taken as the result.

In the artificial leather of the present invention, the overall density of the artificial leather is preferably 0.20 g/cm³ or more and 0.70 g/cm³ or less. Setting the density to 0.20 g/cm³ or more secures moderate resilience of the artificial leather while setting the density to 0.70 g/cm³ or less allows the artificial leather to have good texture. The overall density of the artificial leather is more preferably 0.22 g/cm³ or more and 0.60 g/cm³ or less, still more preferably 0.25 g/cm³ or more and 0.50 g/cm³ or less.

In the present invention, the overall density of the artificial leather refers to a value obtained by calculating the overall density of the artificial leather by the following formula using the mass of a sample of 20 cm×20 cm of the artificial leather and averaging values measured at 10 points.

Overall density of artificial leather (g/cm³)=mass of sample (g)/(20 (cm)×20 (cm)×thickness of sample (cm)).

The thickness of the artificial leather of the present invention is preferably 0.8 mm or more and 4.0 mm or less, more preferably 0.9 mm or more and 3.5 mm or less, from the viewpoint of achieving both of supple flexibility and moderate resilience of the artificial leather.

In the present invention, the thickness of the artificial leather refers to an arithmetic average of values obtained by measuring the thickness at 10 points in the width direction of the artificial leather using a thickness measuring instrument (such as a dial thickness gauge “Peacock Model H” manufactured by OZAKI MFG. CO., LTD.).

It is also preferable for the artificial leather of the present invention to contain, for example, dyes, pigments, softening agents, texture adjustors, pilling prevention agents, antibacterial agents, deodorants, water repellent agents, light resisting agents, and weathering agents.

[Method for Producing Artificial Leather]

Next, a method for producing the artificial leather of the present invention is described below.

The method for producing the artificial leather of the present invention is a method for producing artificial leather that includes, as constituent elements, a nonwoven fabric containing ultrafine fibers having an average single-fiber diameter of 0.1 μm or more and 10 μm or less, and an elastomer, the method preferably including steps (i) to (v) below in this order:

-   -   (i) a step of preparing a nonwoven fabric by entangling         ultrafine fiber-generating fibers containing two or more types         of thermoplastic resins that differ in solubility to a solvent,     -   (ii) a step of impregnating the nonwoven fabric with an aqueous         solution of a water-soluble resin and drying the resultant at         110° C. or more to add the water-soluble resin,     -   (iii) a step of pressing the nonwoven fabric with the         water-soluble resin to provide a sheet,     -   (iv) a step of treating the sheet obtained in step (iii) above         with a solvent to generate ultrafine fibers having an average         fiber diameter of single fibers of 0.1 μm or more and 10 μm or         less and then impregnating the sheet with a solvent solution of         an elastomer and solidifying the resultant to add the elastomer,         or a step of impregnating the sheet obtained in step (iii) above         with a solvent solution of an elastomer and solidifying the         resultant to add the elastomer and then treating the sheet with         a solvent to generate ultrafine fibers having an average fiber         diameter of single fibers of 0.1 μm or more and 10 μm or less,         and     -   (v) a step of forming nap on at least one surface of the sheet         obtained in step (iv) above without dividing the sheet into a         plurality of pieces in a thickness direction.

By performing steps (i) to (v) in this order, it is possible to obtain artificial leather having supple flexibility and moderate resilience.

First, step (i) is described below.

Step (i) is designed to prepare a nonwoven fabric by entangling ultrafine fiber-generating fibers made of two or more types of thermoplastic resins that differ in solubility to a solvent.

The ultrafine fiber-generating fibers are entangled to form a nonwoven fabric in advance, and the fibers are treated to make them ultrafine in subsequent step (iv), thereby providing a nonwoven fabric of entangled ultrafine fibers.

Adoptable ultrafine fiber-generating fibers include: sea-island composite fibers produced by using two thermoplastic resins different in solubility in a solvent as a sea component and an island component and dissolving and removing the sea component by using a solvent or the like to allow the island component to be left to form ultrafine fibers; and splittable type composite fibers produced by alternately disposing two thermoplastic resins so that their cross sections are arranged radially or in layers and then splitting and separating the two components to form ultrafine fibers. In particular, sea-island composite fibers are preferred from the viewpoint of texture and surface quality because the removal of the sea component will leave moderate gaps between pieces of the island component, that is, between ultrafine fibers in each fiber bundle.

The sea-island composite fibers can be produced by using a sea-island type composite spinneret through which two mutually aligned components, that is, the sea component and the island component, are spun in a mutually aligned polymer array or by spinning a mixture of two components, that is, the sea component and the island component, by the blend spinning technique, of which the use of the polymer array spinning method is preferred for the production of the sea-island composite fibers because ultrafine fibers with uniform fineness can be obtained.

If a staple nonwoven fabric is used as the nonwoven fabric, it is preferable for the resulting ultrafine fiber-generating fibers to be crimped and then cut to a predetermined length to provide raw stock. Generally known methods may be used for the crimping and cutting steps.

Then, the resulting raw stock is processed by, for example, a cross lapper to produce a fiber web, which is then subjected to fiber entangling treatment to provide a nonwoven fabric. Usable methods for producing the nonwoven fabric by entangling fiber webs include needle punching and water jet punching.

It is also preferable for the aforementioned nonwoven fabric to be subjected to heat shrinkage treatment with warm water or steam to improve the fine feel of the fibers.

Next, step (ii) is described below.

Step (ii) is designed to impregnate the nonwoven fabric with an aqueous solution of a water-soluble resin and dry it at 110° C. or higher to add the water-soluble resin. This causes migration of the water-soluble resin through the nonwoven fabric so that the resin will be localized near the surfaces of the nonwoven fabric. Adding the water-soluble resin to the nonwoven fabric allows the fibers to be fixed to ensure improved dimensional stability, and the localization of the water-soluble resin near the surfaces of the nonwoven fabric allows the inner parts, where the water-soluble resin content is small and dimensional stability is low, to be pressed preferentially in subsequent step (iii) for compression in the thickness direction, leading to the formation of a structure having lower fiber densities near the surfaces and higher fiber densities in the inner parts. In subsequent step (iv) where an elastomer is added after generating ultrafine fibers, furthermore, the localization of the water-soluble resin near the surfaces leads to a smaller content of the elastomer near the surfaces where the content of the water-soluble resin is large and also leads to a smaller contact area between the ultrafine fibers and the elastomer because their contact is hindered by the water-soluble resin. In the inner parts of the nonwoven fabric where the content of the water-soluble resin is smaller, it is possible to add a larger amount of the elastomer, leading to a larger contact area between the ultrafine fibers and the elastomer.

In the fiber sheet thus produced, both the fiber density and the elastomer density are low and their contact area is small near the surfaces, and accordingly, the surfaces can be nap-raised easily, allowing the production of products with fine, soft-to-the-touch surfaces, so that supple flexibility can be imparted to the artificial leather. In the inner parts, on the other hand, both the fiber density and the elastomer density are high and their contact area is large, so that moderate resilience can be imparted to the artificial leather. By nap-raising at least one surface of the fiber sheet thus obtained without dividing the fiber sheet into a plurality of pieces in step (v), following Formulas (a) and (b), which are important requirements of the present invention, are satisfied.

0.5≤F _(A) /F _(B)<1  (a)

0.5≤F _(C) /F _(B)<1  (b)

where F_(A), F_(B), and F_(C) are respectively the fiber density (g/cm³) in a layer on one surface side, the fiber density (g/cm³) in a layer at the center in the thickness direction, and the fiber density (g/cm³) in a layer on the other surface side when the artificial leather is trisected in the thickness direction.

For the present invention, polyvinyl alcohol with a degree of saponification of 80% or more is preferred as the water-soluble resin.

Usable methods for adding the water-soluble resin to the nonwoven fabric include impregnating the nonwoven fabric with an aqueous solution of the water-soluble resin, followed by drying. The concentration of the water-soluble resin in the aqueous solution is preferably 1% or more and 20% or less. It is important for the drying temperature to be 110° C. or higher to promote migration.

The amount of the water-soluble resin added is preferably 5 mass % or more and 60 mass % or less relative to the nonwoven fabric (sheet) measured immediately before addition. The aforementioned structure can be obtained when the amount is 5 mass % or more, more preferably 10 mass % or more. Setting the amount to 60 mass % or less, more preferably 50 mass % or less, allows the production of an intermediate sheet and artificial leather with high processability and good physical properties including wear resistance.

The water-soluble resin added to the nonwoven fabric is removed using hot water or the like after adding the elastomer in step (iv).

Next, step (iii) is described below.

Step (iii) is designed to press the nonwoven fabric with the water-soluble resin added in the thickness direction to provide a sheet. As described above, it is important that the nonwoven fabric formed of ultrafine fibers to which the water-soluble resin has been added by migration be pressed in the thickness direction. As a result, the inner part of the nonwoven fabric, where the water-soluble resin is less abundant and the ultrafine fibers are not fixed, is pressed preferentially, leading to a higher fiber density in the inner part than that near the surfaces.

The pressing of the nonwoven fabric may be carried out at the same time as calendering or squeezing out the solvent in the treatment of generating ultrafine fibers.

Next, step (iv) is described below.

Step (iv) is designed to add an elastomer to the sheet resulting from step (iii) above by performing treatment thereof with a solvent to generate ultrafine fibers with an average single-fiber diameter of 0.1 μm or more and 10 μm or less and impregnating the sheet with a solution of the elastomer, followed by solidification, or designed to impregnate the sheet resulting from step (iii) above with a solution of the elastomer, followed by solidification, to add the elastomer to the sheet, and then treat the sheet with a solvent to generate ultrafine fibers with an average single-fiber diameter of 0.1 μm or more and 10 μm or less.

The generation of ultrafine fibers is carried out by immersing the nonwoven fabric formed of sea-island composite fibers in a solvent to dissolve and remove the sea component.

In the case where the ultrafine fiber-generating fibers are sea-island composite fibers and where the sea component is polyethylene, polypropylene, or polystyrene, an organic solvent such as toluene and trichloroethylene can be used as the solvent to dissolve and remove the sea component. An aqueous alkali solution of sodium hydroxide or the like can be used when the sea component is, for instance, copolymerized polyester or polylactic acid. Hot water can be used when the sea component is a water-soluble thermoplastic polyvinyl alcohol-based resin.

To fix an elastomer to a sheet of nonwoven fabric, the sheet may be impregnated with a solution of the elastomer and then subjected to wet coagulation or dry coagulation, either of which may be selected appropriately depending on the type of polyurethane used.

Next, step (v) is described below.

Step (v) is designed to perform nap raising on at least one surface of the sheet obtained in step (iv) above to form nap without dividing the sheet into a plurality of pieces in the thickness direction.

The nap raising may be performed on both surfaces. As described above, a surface that is less abundant in fibers and the elastomer can be nap-raised easily to ensure soft-to-the-touch quality.

The nap raising can be performed by grinding with sandpaper, roll sander, or the like. Treatment with a lubricant such as silicone emulsion may be performed before the nap raising. Furthermore, treatment with an antistatic agent before the nap raising is preferred because grinding powder generated from the sheet by grinding is prevented from being deposited on the sandpaper.

According to the present invention, since the fiber densities and the elastomer densities on the napped surface side and the other surface side in the thickness direction are low, nap raising is easily performed, a fine, soft-to-the-touch surface quality is obtained, and supple flexibility can be imparted. By increasing the fiber density and the elastomer density in the layer at the center in the thickness direction, moderate resilience can be imparted to the artificial leather. As a result, it is possible to achieve both of supple flexibility and moderate resilience and to suppress occurrence of creases and looseness at the time of bending the sheet.

The artificial leather of the present invention can be dyed. An appropriate dye may be selected to meet the properties of the ultrafine fibers in the artificial leather. For example, a disperse dye may be used for ultrafine fibers of polyester while an acidic dye or premetallized dye may be used for ultrafine fibers of polyamide fibers. In the case where the dyeing is carried out with a disperse dye, it is preferable to perform reduction cleaning after dyeing.

It is also preferable to use a dyeing assistant with the aim of improving dyeing uniformity and reproducibility.

Furthermore, the artificial leather of the present invention may be treated with a finishing agent such as a softening agent, such as silicone, and an antistatic agent. Finishing treatment may be performed after dyeing or simultaneously with dyeing in the same bath.

Furthermore, a resin layer can be formed on the artificial leather of the present invention. Examples of the method for forming the resin layer in the present invention include a method in which the resin layer is formed by applying the resin by a screen method such as a flat screen or a rotary screen, a gravure coating method, or the like and then drying the resin layer, and a method in which a resin film is continuously or discontinuously formed on support substrate fibers such as release paper, then an adhesive is applied to a surface of the resin film, the resin film is bonded to a surface to be a fiber structure, and the release paper is peeled off to form the resin layer.

In the present invention, it is preferable that the resin layer is applied so as to be discontinuously formed on the surface layer of the napped surface of the artificial leather. Furthermore, in order to form two or three resin layers, the resin layers can be formed by repeating the above method twice or three times. As for the above method, the same method may be repeated, or two or more methods may be used in combination.

Further, designability can be imparted to a surface of the artificial leather as necessary. For example, the surface may be subjected to post processing including boring such as perforation, embossing, laser processing, pinsonic processing, and printing processing.

EXAMPLES

Next, the artificial leather of the present invention is described with reference to examples. For matters not specifically described, measurement was performed according to the above method.

<Fiber Density in Layer>

A sample measuring 20 cm×20 cm of the obtained artificial leather was trisected into a layer (A) on one surface side, a layer (B) at the center in the thickness direction, and a layer (C) on the other surface side in the thickness direction using a slicer. The thickness of the trisected sample was measured at a magnification of 200 times using a scanning electron microscope, and it was confirmed that the three samples had equal thicknesses. Then, the divided sample was immersed in N,N-dimethylformamide for eight hours to completely extract the elastomer. Thereafter, N,N-dimethylformamide contained in the sample was washed away with water, and the sample was sufficiently dried with a hot air dryer under the condition of 100° C.×20 minutes. The mass of the dried sample was measured, and the fiber density in each layer was calculated by the following formula.

Fiber density (g/cm³)=mass of sample after extraction (g)/(20 (cm)×20 (cm)×thickness of sample before extraction (cm))

For the thickness of the sample before extraction in the calculation of the fiber density, 10 images of different portions of a cross section of the sample before extraction were photographed at a magnification of 200 times using a scanning electron microscope, and the thickness of the sample was determined from each of these photographed images. When the sample had a nap layer, the thickness excluding the thickness of the nap layer was taken as the thickness of the sample.

Using the calculated F_(A), F_(B), and F_(C), the fiber density ratio (F_(A)/F_(B) or F_(C)/F_(B)) was calculated, and the average of the values measured at 10 points was taken as the result.

<Elastomer Density in Layer>

A sample measuring 20 cm×20 cm of the obtained artificial leather was trisected into a layer (A) on one surface side, a layer (B) at the center in the thickness direction, and a layer (C) on the other surface side in the thickness direction using a slicer. The thickness of the trisected sample was measured, and it was confirmed that the three samples had equal thicknesses. Then, the divided sample was immersed in N,N-dimethylformamide for eight hours to completely extract the elastomer. Thereafter, N,N-dimethylformamide contained in the sample was washed away with water, and the sample was sufficiently dried with a hot air dryer under the condition of 100° C.×20 minutes. The mass of the dried sample was measured, and the elastomer density in each layer was calculated by the following formula.

Elastomer density (g/cm³)=(mass of sample before extraction (g)−mass of sample after extraction (g))/(20 (cm)×20 (cm)×thickness of sample before extraction (cm))

For the thickness of the sample before extraction in the calculation of the elastomer density, 10 images of different portions of a cross section of the sample before extraction were photographed at a magnification of 200 times using a scanning electron microscope, and the thickness of the sample was determined from each of these photographed images. When the sample had a nap layer, the thickness excluding the thickness of the nap layer was taken as the thickness of the sample.

Using the calculated P_(A), P_(B), and P_(C), the elastomer density ratio (P_(A)/P_(B) or P_(C)/P_(B)) was calculated, and the average of the values measured at 10 points was taken as the result.

<Evaluation Methods>

(1) Surface Quality:

The quality was rated as 5 to 1 shown below on the basis of visual inspection and sensory evaluation by a total of 20 raters made up of 10 healthy male adults and 10 healthy female adults. The rating given by the greatest number of raters was taken as the final rating in external appearance quality. A sample that obtained a rating of 4 or higher was judged as good.

5: Fibers are dispersed suitably and soft to the touch.

4: Intermediate between 3 and 5

3: Fibers are not dispersed suitably in some parts but soft to the touch.

2: Intermediate between 1 and 3

1: Fibers are very poorly dispersed overall and rough to the touch.

(2) Flexibility:

The quality was rated as 5 to 1 shown below on the basis of sensory evaluation by a total of 20 raters made up of 10 healthy male adults and 10 healthy female adults. The rating given by the greatest number of raters was taken as the final rating in external appearance quality. A sample that obtained a rating of 4 or higher was judged as good.

5: The sample follows deformation in a supple manner and has a soft tactile sensation.

4: Intermediate between 3 and 5

3: The sample slightly poorly follows deformation but has a soft tactile sensation.

2: Intermediate between 1 and 3

1: The sample is bent when deformed and has a hard tactile sensation.

(3) Resilience:

The quality was rated as 5 to 1 shown below on the basis of sensory evaluation by a total of 20 raters made up of 10 healthy male adults and 10 healthy female adults. The rating given by the greatest number of raters was taken as the final rating in external appearance quality. A sample that obtained a rating of 4 or higher was judged as good.

5: The sample returns to the original state when deformed, and a hard portion is felt when gripped.

4: Intermediate between 3 and 5

3: The sample tends to return to the original state when deformed but cannot completely return to the original state, and a hard portion is slightly felt when gripped.

2: Intermediate between 1 and 3

1: The sample does not return from the deformed state, and no hard portion is felt when gripped.

(4) Creases and Looseness when Bent:

The quality was rated as 5 to 1 shown below on the basis of sensory evaluation by a total of 20 raters made up of 10 healthy male adults and 10 healthy female adults. The rating given by the greatest number of raters was taken as the final rating in external appearance quality. A sample that obtained a rating of 4 or higher was judged as good.

5: Even when the sample is bent, there is no conspicuous wrinkle or looseness of the sheet.

4: Intermediate between 3 and 5

3: When the sample is bent, slight wrinkles are observed, but there is no looseness of the sheet.

2: Intermediate between 1 and 3

1: When the sample is bent, wrinkles are clearly observed, and the sheet is loose.

<Abbreviations of Chemical Substances>

-   -   PET: polyethylene terephthalate     -   PU: polyurethane     -   MDI: 4,4′-diphenylmethane diisocyanate     -   DMF: N,N-dimethylformamide     -   PVA: polyvinyl alcohol

<Ultrafine Fiber Resin>

(1) Polyethylene Terephthalate A (PET-A)

-   -   Ethylene glycol: derived from petroleum resources     -   Terephthalic acid: derived from petroleum resources     -   Biomass plastic content: 0%

(2) Polyethylene Terephthalate B (PET-B)

-   -   Ethylene glycol: derived from biomass resources     -   Terephthalic acid: derived from petroleum resources     -   Biomass plastic content: 31%

<Elastomer>

(1) Polycarbonate-Based Polyurethane A (PU-A)

-   -   Polyol: polycarbonate diol (derived from petroleum resources)     -   Polyisocyanate: MDI     -   Chain extender: EG     -   Biomass plastic content: 0%

(2) Polycarbonate-Based Polyurethane B (PU-B)

-   -   Polyol: polycarbonate diol (derived from biomass resources)     -   Polyisocyanate: MDI     -   Chain extender: EG     -   Biomass plastic content: 38%

Example 1

(Raw Stock)

Polyethylene terephthalate A (PET-A) adopted as the island component and polystyrene adopted as the sea component were subjected to melt spinning using a sea-island composite spinneret having 16 islands per hole under the conditions of a spinning temperature of 280° C., an island/sea mass ratio of 55/45, a discharge rate of 1.3 g/min·hole, and a spinning speed of 1,300 m/min. Subsequently, 3.6-fold stretching was performed in a 90° C. oil bath designed for spinning, and crimping was performed using a stuffer box crimper, followed by cutting to a length of 51 mm to provide raw stock of sea-island composite fibers with an average direct fiber diameter of ultrafine fibers, which are the island component, of 3.5 μm.

(Entanglement)

The raw stock thus obtained was subjected to carding and cross-lapping to produce a laminated fiber web, which was then subjected to needle punching at a rate of 3,500 punches/cm² to provide an entangled fiber sheet (felt) with a thickness of 4.2 mm and a density of 0.20 g/cm³.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing)

The entangled fiber sheet thus obtained was subjected to shrinkage treatment in hot water at a temperature of 96° C., impregnated with a 12 mass % aqueous solution of PVA with a degree of saponification of 88%, squeezed so that the solid content relative to the fibers would reach a target value of 40 mass %, and dried in hot air at a temperature of 140° C. for 10 minutes while promoting the migration of PVA, thereby providing a sheet containing PVA. The sheet containing PVA thus obtained was immersed in trichloroethylene and subjected to 10 repetitions of liquid squeezing and pressing with a mangle to carry out dissolution and removal of the sea component and pressing of the sheet containing PVA, thereby providing a sea-free, PVA-containing sheet that contains entangled ultrafine fiber bundles carrying PVA.

(Addition of Elastomer)

The sea-free, PVA-containing pressed sheet thus obtained was impregnated with a DMF solution of polyurethane A (PU-A) adjusted to a solid content of 15 mass %, and squeezed so that the solid content relative to the fibers would reach a target value of 50 mass %, followed by coagulating the polyurethane in a 30 mass % aqueous solution of DMF. Subsequently, PVA and DMF were removed in hot water, and drying was performed in hot air at a temperature of 110° C. for 10 minutes to provide a sheet containing polyurethane.

(Nap Raising)

One surface of the sheet containing polyurethane thus obtained was ground with endless sandpaper with a sandpaper grit number of 240 to produce a napped surface while adjusting the thickness simultaneously, thereby providing a napped sheet with a thickness of 2.70 mm.

(Dyeing)

The napped sheet thus obtained was dyed using a jet dyeing machine at a temperature of 120° C. and dried using a drying machine, thereby providing artificial leather.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 1.

Example 2

(Raw Stock)

Raw stock of sea-island composite fibers was obtained in the same manner as in Example 1.

(Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 1 except that the thickness was changed to 4.7 mm and the density was changed to 0.18 g/cm³.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing Up to Addition of Elastomer)

In the same manner as in Example 1, a sheet containing polyurethane was obtained.

(Nap Raising)

A napped sheet was obtained in the same manner as in Example 1 except that the thickness was changed to 2.75 mm.

(Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 1.

Example 3

(Raw Stock)

Raw stock of sea-island composite fibers was obtained in the same manner as in Example 1.

(Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 1 except that the thickness was changed to 2.6 mm and the density was changed to 0.19 g/cm³.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing Up to Addition of Elastomer)

In the same manner as in Example 1, a sheet containing polyurethane was obtained.

(Nap Raising)

A napped sheet was obtained in the same manner as in Example 1 except that the thickness was changed to 1.60 mm.

(Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 1.

Example 4

(Raw Stock)

Polyethylene terephthalate B (PET-B) adopted as the island component and polystyrene adopted as the sea component were subjected to melt spinning using a sea-island composite spinneret having 16 islands per hole under the conditions of a spinning temperature of 285° C., an island/sea mass ratio of 80/20, a discharge rate of 1.2 g/min·hole, and a spinning speed of 1,100 m/min. Subsequently, 2.8-fold stretching was performed in a 90° C. oil bath designed for spinning, and crimping was performed using a stuffer box crimper, followed by cutting to a length of 51 mm to provide raw stock of sea-island composite fibers with an average direct fiber diameter of ultrafine fibers, which are the island component, of 5.0 μm.

(Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 1 except that the thickness was changed to 2.3 mm and the density was changed to 0.25 g/cm³.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing)

A sea-free, PVA-containing sheet was obtained in the same manner as in Example 1 except that the target addition amount was changed to 30 mass %.

(Addition of Elastomer)

The sea-free, PVA-containing pressed sheet thus obtained was impregnated with a DMF solution of polyurethane A (PU-A) adjusted to a solid content of 12 mass %, and squeezed so that the solid content relative to the fibers would reach a target value of 30 mass %, followed by coagulating the polyurethane in a 30 mass % aqueous solution of DMF. Subsequently, PVA and DMF were removed in hot water, and drying was performed in hot air at a temperature of 110° C. for 10 minutes to provide a sheet containing polyurethane.

(Nap Raising)

A napped sheet was obtained in the same manner as in Example 1 except that the thickness was changed to 1.35 mm.

(Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 1.

Example 5

(Raw Stock)

Raw stock of sea-island composite fibers was obtained in the same manner as in Example 4.

(Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 1 except that the thickness was changed to 2.4 mm and the density was changed to 0.24 g/cm³.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing)

In the same manner as in Example 4, a sea-free, PVA-containing sheet was obtained.

(Addition of Elastomer)

A sheet containing polyurethane was obtained in the same manner as in Example 4 except that polyurethane B (PU-B) was used.

(Nap Raising)

A napped sheet was obtained in the same manner as in Example 1 except that the thickness was changed to 1.45 mm.

(Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 1.

Example 6

(Raw Stock)

Raw stock of sea-island composite fibers was obtained in the same manner as in Example 4.

(Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 1 except that the thickness was changed to 2.4 mm and the density was changed to 0.24 g/cm³.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing Up to Addition of Elastomer)

In the same manner as in Example 4, a sheet containing polyurethane was obtained.

(Nap Raising)

A napped sheet was obtained in the same manner as in Example 1 except that the thickness was changed to 1.30 mm.

(Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 1.

Example 7

(Raw Stock)

Polyethylene terephthalate A (PET-A) adopted as the island component and polystyrene adopted as the sea component were subjected to melt spinning using a sea-island composite spinneret having 200 islands per hole under the conditions of a spinning temperature of 280° C., an island/sea mass ratio of 60/40, a discharge rate of 1.1 g/min·hole, and a spinning speed of 1,300 m/min. Subsequently, 2.8-fold stretching was performed in a 90° C. oil bath designed for spinning, and crimping was performed using a stuffer box crimper, followed by cutting to a length of 51 mm to provide raw stock of sea-island composite fibers with an average direct fiber diameter of ultrafine fibers, which are the island component, of 0.7 μm.

(Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 1 except that the thickness was changed to 2.0 mm and the density was changed to 0.22 g/cm³.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing Up to Addition of Elastomer)

In the same manner as in Example 4, a sheet containing polyurethane was obtained.

(Nap Raising)

A napped sheet was obtained in the same manner as in Example 1 except that the thickness was changed to 1.15 mm.

(Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 1.

TABLE 1 Example Example Example Example Example Example Example 1 2 3 4 5 6 7 Ultrafine fiber resin PET-A PET-A PET-A PET-B PET-B PET-B PET-B Elastomer PU-A PU-A PU-A PU-A PU-B PU-A PU-A Average single-fiber 3.5 3.5 3.5 5.0 5.0 5.0 0.7 diameter of ultrafine fiber [μm] F_(A)/F_(B) [—] 0.81 0.65 0.76 0.72 0.60 0.90 0.70 F_(C)/F_(B) [—] 0.78 0.61 0.73 0.70 0.63 0.92 0.70 P_(A)/P_(B) [—] 0.79 0.71 0.85 0.73 0.65 0.88 0.85 P_(C)/P_(B) [—] 0.77 0.72 0.81 0.71 0.68 0.90 0.81 Overall density of 0.32 0.30 0.31 0.36 0.34 0.35 0.35 artificial leather [g/cm³] Thickness of 2.80 2.85 1.70 1.45 1.55 1.40 1.25 artificial leather [mm] Biomass plastic 0 0 0 31 31 31 0 content of nonwoven fabric [%] Biomass plastic 0 0 0 0 38 0 0 content of elastomer [%] Biomass plastic 0 0 0 23 33 23 0 content of artificial leather [%] Surface quality 5 5 5 4 4 4 5 Flexibility 4 4 5 5 5 4 5 Resilience 5 5 5 4 4 4 4 Creases and looseness 4 4 5 5 5 4 5 when bent

Comparative Example 1

(Raw Stock Up to Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 1.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing)

A sea-free, PVA-containing sheet was produced in the same manner as in Example 1 except that in the addition of PVA, drying was performed in hot air at a temperature of 100° C. for 30 minutes while depressing the migration of PVA and that the PVA-containing sheet was immersed in trichloroethylene to remove the sea component without liquid squeezing and pressing with a mangle.

(Addition of Elastomer Up to Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a poor surface quality, poor flexibility, and little resilience and had conspicuous creases and looseness when bent. The results are shown in Table 2.

Comparative Example 2

(Raw Stock Up to Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 1.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing)

A sea-free, PVA-containing sheet was produced in the same manner as in Example 1 except that in the addition of PVA, drying was performed in hot air at a temperature of 140° C. for 10 minutes while allowing the migration of PVA and that the PVA-containing sheet was immersed in trichloroethylene to remove the sea component without liquid squeezing and pressing with a mangle.

(Addition of Elastomer Up to Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a poor surface quality and poor flexibility but had conspicuous creases and looseness when bent while having resilience. The results are shown in Table 2.

Comparative Example 3

(Raw Stock to Addition of Elastomer)

In the same manner as in Example 1, a sheet containing polyurethane was obtained.

(Nap Raising)

A napped sheet having a thickness of 1.45 mm was obtained in the same manner as in Example 1 except that the sheet containing polyurethane was half-cut in the thickness direction, and the surface opposite to the half-cut surface was nap-raised.

(Dyeing)

Artificial leather was obtained in the same manner as in Example 1.

The obtained artificial leather had a good surface quality, poor flexibility, and little resilience and had slightly conspicuous creases when bent. The results are shown in Table 2.

Comparative Example 4

(Raw Stock Up to Entanglement)

An entangled fiber sheet (felt) was obtained in the same manner as in Example 4.

(Addition of Water-Soluble Resin, Sea Removal, and Pressing)

A sea-free, PVA-containing sheet was produced in the same manner as in Example 4 except that in the addition of PVA, drying was performed in hot air at a temperature of 100° C. for 30 minutes while depressing the migration of PVA and that the PVA-containing sheet was immersed in trichloroethylene to remove the sea component without liquid squeezing and pressing with a mangle.

(Addition of Elastomer Up to Dyeing)

Artificial leather was obtained in the same manner as in Example 4.

The obtained artificial leather had a poor surface quality, poor flexibility, and little resilience and had conspicuous creases and looseness when bent. The results are shown in Table 2.

TABLE 2 Compar- Compar- Compar- Compar- ative ative ative ative Example 1 Example 2 Example 3 Example 4 Ultrafine fiber resin PET-A PET-A PET-A PET-B Elastomer PU-A PU-A PU-A PU-A Average single-fiber 3.5 3.5 3.5 5.0 diameter of ultrafine fiber [μm] F_(A)/F_(B) [—] 1.10 1.06 0.90 1.15 F_(C)/F_(B) [—] 1.13 1.10 1.50 1.10 P_(A)/P_(B) [—] 1.15 0.92 0.87 1.10 P_(C)/P_(B) [—] 1.10 0.95 1.45 1.05 Overall density of 0.31 0.30 0.31 0.35 artificial leather [g/cm³] Thickness of 2.82 2.88 1.35 1.50 artificial leather [mm] Biomass plastic 0 0 0 31 content of nonwoven fabric [%] Biomass plastic 0 0 0 0 content of elastomer [%] Biomass plastic 0 0 0 23 content of artificial leather [%] Surface quality 3 3 4 3 Flexibility 3 3 3 3 Resilience 3 4 3 3 Creases and looseness 2 2 3 2 when bent

Example 8

(Raw Stock Up to Dying)

Artificial leather was obtained in the same manner as in Example 1.

(Formation of Resin Layer)

A rotary coating method was repeated three times on the napped surface of the sheet obtained in the above step to form a polyurethane resin layer composed of three discontinuous layers on the surface, thereby obtaining artificial leather. On the surface, resin layer portions were scattered in an island shape, and the resin layer was discontinuously present.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 3.

Example 9

(Raw Stock Up to Dying)

Artificial leather was obtained in the same manner as in Example 4.

(Formation of Resin Layer)

Artificial leather was obtained in the same manner as in Example 8.

The obtained artificial leather had a good surface quality, supple flexibility, and moderate resilience and had no creases or looseness when bent. The results are shown in Table 3.

Comparative Example 5

(Raw Stock Up to Dying)

Artificial leather was obtained in the same manner as in Comparative Example 1.

(Formation of Resin Layer)

Artificial leather was obtained in the same manner as in Example 8.

The obtained artificial leather had a poor surface quality, poor flexibility, and little resilience and had conspicuous creases and looseness when bent. The results are shown in Table 3.

TABLE 3 Comparative Example 8 Example 9 Example 5 Ultrafine fiber resin PET-A PET-B PET-A Elastomer PU-A PU-A PU-A Thickness of resin layer [μm] 0.10 0.10 0.10 Average single-fiber diameter of 3.5 5.0 3.5 ultrafine fiber [μm] F_(A)/F_(B) [—] 0.86 0.78 1.20 F_(C)/F_(B) [—] 0.84 0.76 1.20 Overall density of artificial 0.35 0.41 0.36 leather [g/cm³] Thickness of artificial leather 2.70 1.30 2.72 [mm] Biomass plastic content of 0 31 0 nonwoven fabric [%] Biomass plastic content of 0 0 0 elastomer [%] Biomass plastic content of resin 0 0 0 layer [%] Biomass plastic content of 0 21 0 artificial leather [%] Surface quality 5 4 3 Flexibility 4 5 3 Resilience 5 4 3 Creases and looseness when bent 4 5 2

DESCRIPTION OF REFERENCE SIGNS

-   -   1: Nap layer     -   2: Resin layer     -   11: Artificial leather     -   A, D: Layer on one surface side     -   B, E: Layer at center in thickness direction     -   C, F: Layer on other surface side 

1. Artificial leather comprising, as constituent elements: a nonwoven fabric containing ultrafine fibers having an average single-fiber diameter of 0.1 μm or more and 10 μm or less; and an elastomer, the artificial leather satisfying Formulas (a) and (b) below: 0.5≤F _(A) /F _(B)<1  (a) 0.5≤F _(C) /F _(B)<1  (b) where F_(A), F_(B), and F_(C) are respectively a fiber density (g/cm³) in a layer on one surface side, a fiber density (g/cm³) in a layer at a center in a thickness direction, and a fiber density (g/cm³) in a layer on another surface side when the artificial leather is trisected in the thickness direction.
 2. The artificial leather according to claim 1, further comprising at least one nap layer formed by nap raising.
 3. The artificial leather according to claim 1 or 2, further comprising at least one resin layer.
 4. The artificial leather according to claim 3, wherein the resin layer is discontinuously formed in a surface of the artificial leather.
 5. The artificial leather according to claim 1 or 2, further satisfying Formulas (c) and (d) below: 0.6≤P _(A) /P _(B)<1  (c) 0.6≤P _(C) /P _(B)<1  (d) where P_(A), P_(B), and P_(C) are respectively an elastomer density (g/cm³) in the layer on the one surface side, an elastomer density (g/cm³) in the layer at the center in the thickness direction, and an elastomer density (g/cm³) in the layer on the other surface side when the artificial leather is trisected in the thickness direction.
 6. The artificial leather according to claim 1, wherein an overall density of the artificial leather is 0.2 g/cm³ or more and 0.7 g/cm³ or less.
 7. The artificial leather according to claim 1, wherein a thickness of the artificial leather is 0.8 mm or more and 4.0 mm or less. 